1. Field of the Invention
The present invention relates to the technical field of transfer switches, for use with portable or stationary electric generators. In particular, the present invention is directed to an automatic transfer switch apparatus.
2. Background
Transfer switches, for use in association with portable or stand-alone electrical generators, are known in the prior art.
A private residence, for example, may normally receive its electrical power from a utility company. For various reasons, however (location in a region prone to severe weather, etc.), the homeowner may desire a back-up source of electrical power, so that comfort or at least habitability of the residence can be maintained, during periods in which utility power is unavailable.
Typically, a gasoline, diesel, propane or natural gas internal combustion engine-powered electrical generator, capable of generating split-phase alternating voltage, may be installed in or near the residence, and arranged to be connected to one or more of the electrical circuits in the residence in order to provide the desired back-up power.
However, one cannot simply leave the back-up generator permanently connected, in parallel with the utility power, to the residential electrical circuits, nor can one simply connect and power up a back-up generator, without first disconnecting the residential circuits from the power lines coming in from the utility. The reason for this is the possibility that some of the current generated by the back-up generator may inadvertently be backfed into the utility power lines, which may lead to personal injury and/or damage to utility equipment (transformers, etc.).
Transfer switches have been provided to establish the electrical connections between the utility, the residential circuit(s) and the back-up generator. Prior art residential transfer switches typically have been manually actuated devices; known as “break, then make” switches. This means that when the switch is thrown, the connection between the residential circuit(s) and whichever current source is at the time actually connected to the residential circuit, is broken, before the connection is made between the residential circuit, and the current source which is being substituted in.
In a typical situation, utility power fails or falls drastically. The residence owner proceeds to start up the back-up generator, and once operating speed and voltage have been attained, the switch is manually thrown, to disconnect the utility from the residential circuit, and thereafter, cut in the current from the back-up generator.
Prior art manual transfer switches are capable of providing the simple function of serving to safely accomplish the substitution of power sources. However, such prior art manual switches require the presence of the homeowner, in order to accomplish the transfer. This may be undesirable, in that some appliances (e.g., refrigerator or freezer, sump pump, etc.) should not go without power for extended periods of time. If a homeowner is absent for more than an hour or two, continued power outages may cause potentially serious damage or injury to equipment, property, pets, etc.
Accordingly, it would be desirable to provide a transfer switch for residential/small business environments and the like, that is capable of actuating automatically, upon sensing a sustained interruption of utility-supplied electrical power.
It would also be desirable to provide an automatic transfer switch, that is capable of starting a back-up generator, upon sensing a sustained interruption of utility-supplied electrical power, and disconnecting the utility and connecting the back-up, when the back-up generator is capable of assuming the load.
These and other desirable characteristics of the invention will become apparent in light of the present specification, claims and drawings.